This is a request for the purchase of a LaserMat (Finnigan MAT, San Jose, California) laser desorption mass spectrometer (LDMS). Results obtained from this instrument will complement those obtained from other analytical instruments available at The Salk Institute, for the characterization of biopolymers including peptides/proteins, nucleic acids, and oligosaccharides. Other instruments already available include a mass spectrometer fitted with a liquid secondary ionization source, gas phase sequencers with PTH analyzers, and a full computerized HPLC-based amino acid analyzer. The major user group will consist of seven investigators and A. Craig, whose expertise in mass spectrometry is well acknowledged (see biosketch). The individual users at The Salk Institute and neighboring academic institutions will focus on the use of LDMS to screen novel hormones, toxins, growth factors, and other molecules, and their posttranslational modifications. The requested instrument is needed to complement the strong, classical, Edman degradation approach at The Salk Institute and facilitate, because of its greater sensitivity, more accurate mass measurements with the JEOL HX110 MS. A second independent focus is the application of mass spectrometry to study protein-protein interactions including ligand receptor binding site, stoichiometry, and specificity.